Telephone system



March 23 1926.

- A. H. DYSON TELEPHONE SYSTEM Filed Jan. 5, 1905 8 Sheets-Sheet l March 23 1926.

A. H. DYSON TELEPHONE SYSTEM Filed Jan. 5,

1905 SSheetS-Sheet' 2 A. H. DYSON TELEPHONE SYSTEM March 23 1926 1.905 8 Sheets-Sheet 5 Filed Jan. 5

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Lvmm NW km March 23 1 926.

8 Shets-Sheet 4 March 23 1926.

A. H. DYSON TELEPHONE SYSTEM Filed Jan. 5, 1905 8 Sheets-Sheet 5 Wig Maa'ch 23 9 126.

' A. H. DYSON TELEPHONE SYSTEM Filed Jan. 5, 1905 8 Sheets-Sheet 6 March 23 1926a;

A. H. DYSON TELEPHONE SYSTEM 8 Sheets-Sheet 7 Filed Jan 5 Marh 23,1926. fi,578,38

* A. H. DYSON TELEPHONE SYSTEM Filed Jan. 5, 1905 s Sheets-Sheet 8 Patented Mar. 23, 1926.

UNITED STATES $78,938 PATENT l ALFRED H. DYSON, 6F CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNEENI'S, T9

AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION 01 DELA- WARE.

TELEPHONE SYSTEM.

Z '0 all whom it may conceive:

Be it known that I, ALFRED H. DYsoN, a citizen of the United States of America, and resident of Chicago, in the county of (look and State of Illinois, have invented a cor lain new and useful Improvement in Telephone Systems, of which the following is a specification.

My invention relates to automatic telephone systems in general; and it relates more particularly to automatic telephone systems in which the different subscribers lines terminate in step-by-step switching mechanism or apparatus, said mechanism or apparatus being under the control of and employed by the subscribers, through the medium of suitable circuit-controlling devices at the subscribers stations, for automatically establshing connection between any calling subscribers line and any desired called subscribers line; and it also relates more especially to automatic telephone systems of the said particular character in which the switching mechanism or apparatus comprises a suitable number of so-called selector-switches, through the medium of which any calling subscriber may establish connection with one or more trunk-lines, and comprising also a suitable number of socalled -connector-switches, through the medium of which a calling subscriber may, after having established the desired trunkline connection, then make the final connection with the line of the called subscriber.

Generally stated, the object ofv my invention is to provide an improved automatic telephone system which will allord eflicient and satisfactory service to different subscribers, and which will, at the same time, be more economical to install and maintain.

A special object is to provide an improved construction and arrangement whereby, in an automatic telephone system of any suitable character, the current, both for talking and signaling purposes, may be furnished from a common battery or other centralized source of current supply.

Another object is to provide an improved construction and arrangement whereby the current for both talking and signaling purposes may, in an automatic telephone system of the character to which my invention more particularly and especially relates, be furnished to the subscribers lines through the said so-called connector-switches,. and

from a common battery or other centralized source of current supply.

Another object, and one which constitutes a distinguishing and more or less specific feature of my invention, is to provide an improved construction and arrangement of such character that no-closed metallic battery circuit will, in the process of connecting up one subscriber with another, be formed or established until the called subscriber answers the call.

Another object is to provide an improved construction and arrangement for releasing the switching mechanism and apparatus employed for connecting up one subscriber with another-that is to say, for restoring said switching mechanism or apparatus to its normal condition, and thus efiecting a disconnection between subscribers lines after the conversation is terminated.

An additional object is to provide an improved construction and arrangement for insuring the automatic removal 0r cutting off of certain bridges from the talking circuit, so that these bridges, which normally exist across the line conductors, and which contain the coils of relays or magnets, may be eliminated from the circuit during conversation between the subscribers, and are thus prevented from remaining across the talking circuit while the calling subscriber is completing the process of making connection with the called subscribers line, and

wvhile the voice currents are traversing the finally established talking circuit.

It is also an object to provide certain details and novel features of construction, and certain features of improvement tending to increase the general, efiiciency and serviceability of an automatic telephone system of this particular character. I

' To the foregoing and other useful ends, my invention consists, in. matters hereinaftel: set forth and claimed.

In the accompanying- "drawings, the first four figures constitute a single diagram illustrait-ing a calling subscribers telephone and switching and signaling equipment connected with a similar equipment of a called subscribers line; Fig. 1 beinga diagrammatic representation of the calling subscribers apparatus. and of the so-called first selector-switch; Fig. 2 being a diagrammatic representation of that portion of the apparatus known as a second selectortor;

.the impu arrangement shown, the impulse switch; Fi 3 being a diagrammatic representation 0 that portion of the switching apparatus known as the connector-switch; Fig. 4 being a diagrammatic representation of the called subscribers telephone and signaling equipment, and of the so-called first selector-switch allotted to the said called subscriber; Fig. 5 being a diagrammatic perspective view of the first-selector; Fig. 6 bem a similar view of the second-selecig. 7 being a similar view of. the connector; and Fig. 8 being a simplified diagram showing the method of supplying talking current to the talking circuit formed between the calling and called subscribers stations.

As thus illustrated, it has been assumed that the subscribers station A is numbered 3321, while the subscribers station B is numbered 2241. In an exchange of this size, it will be readily understood that the arrangement and division of switching apparatus, and of the line terminals, is of. such charis water as to necessitate, or at least make desirab le, the employment of the said first and second selector-switches, as will hereinaf ter more fully appear. With the arrangement shown, each so-calle first selector-switch is allotted to .a single subscribers line, while the so-called connectorswitches are common to the difierent subscribers. .In other words, in the particular system, in connection wlth which I have e ected to illustrate my invention, there are as many so-called first selector-switches as there are subscribers; but the second sele'ctor-switches are common to the different subscribers, and are considerably less in number than the total number of subscribers; and the said so-called connector-switches are also considerably less in number than the total number of subscribers. In the arrangement shown, and as previously stated, a first selector-switch always receives at least the first impulse or impu ses. representing the first di 'itof the called number-that is to'say, this so-called first selector-switch does not operate until the calling subscriber actually begins the process of calling the desired number, and not until se or impulses representing at least the firstdigit of the called number traverse the line of the calling subscriber; and this is thoughtto be the true sense or meaning of the term first selector. Also, with the or impulses representing the next digitof the called "mitted to act u on the said switch; and in t is way the. said so-called number may cause the so-called second selector to operate and accomplish the second step in the process of connecting one subscrlbers line with another. The-impulses representing the last two digits of the called number are, however, received and perarticular connector apnoea at station A includes the usual transmitter and receiver, a call-bell, ahook-switch, and switching mechanism for calling and ringing any other subscriber of the exchan e, as-wil hereinafter more fully appear; an this may also-be true of the apparatus at. station B.

The first selector may. be of any suitable known or approved construction, and may comprise the usual vertical and rotary relays 87 and 90, the bridge cut-ofl' relay 51.

the calling su scriber in establishing the rotary and vertical magnets114 and 109, together with the release magnet 118 and private magnet 106. Other familiar features of a switch of this character consist of the rotary switch-shaft C, which is given a step-by-step vertical movement by the vertical magnet 114, and a ste -by-step rotar movement by the rotary magnet 109, through the medium of any suitable, known or appproved mechanical connections. This first selector-switch is ,also further identified by the circuit-changing arms '63,

64. 65, 66 and 67 com rised in a so-called side-switch, and whic are operated in the usual and well-known manner by the .pri-

vate magnet 106 through the medium of any suitable, known or approved mechanical connections. In, this selector the sideswitch circuit-changing arm 64 has a new function, inasmuch as it cooperates with the wipers 126 in closing the circuit of the release-ma ct 118, these additional wipers 126, having no other function than that of closing the release-circuit, being new in a switch of this character.

The second selector shown in Fig. 2

may also be of any suitable, knownor a proved construction. It may comprise t e usual vertical and rotary relays 184 and 190, the usual private-magnet 500 for operating the so-called side-switch, and the side-switch circuit-changing arms 147, 148, 149, 150 and 151. Other familiar elements of a second selector of this character consist of the vertical magnet 204 and the rotary-magnet 198. together with the releasemagnet, 143. The vertically movable and rotary switch-shaft D is of the usual con-' struction, and maybe operated in the usual or any other suitable manner by the said magnets 198 and 204, the mechanism of this second selector, like that of the first selector, operating on the well-known step-b step principle. In this case, however t e side-switc arm 148 has a new function, inasmuch as it cooperates with the shaftwipers .207 in closingv the release-circuit-that is to say, the. circuit including the release-magnet 143. These additional wipers 207, having no other "function than relay 301, and the ama s that of closing the release-circuit, constitute an additional and new feature in a switch of this character.

The connector shown in Fig. 3 operates on the step-by step principle, like the other switches, in a well-known manner, and may be of any suitable, known or approved character; but in this case certain novel circuit arrangements and features of construction are provided 'in addition to the elementsor features usually found in a connectorswitch of this character. For example, the said connector may comprise the usual vertical and rotary relays 225 and 235, the latter preferably of, say, ance; the release-magnet 254, the ringing private-magnet 32!). Other familar elements in a switch of this character consist of the vertical and r0- tary magnets 349 and 359, which are employed for operating the vertically-movable and'rotary switch-shaft E, the latter being provided with the wipers 350, 360 and 381. The connector is further identified by the circuit-changing arms 322, 323, 32 and 325, of the side-switch that is operated by the private-magnet 329. There are also certain novel elements or features, however, included in the construction of the said connector. For example, the differential release-relay F, used only by the called subscriber as a means of releasing the connections, constitutes a new feature in a connector or" this character. The differential release-relay G, used only when the called subscriber fails to hang up his receiver, also constitutes a novel feature in a switch of this character. @ther novel teatures consist of the impedance-coil 250, which is preferably of 250 ohms resistance; the control-relay H. which is only energized whenthe called subscriber answers; and certain novel circuit arrangements, as will hereinafter more fully appear.

@ne of the principal features of novelty, however. consists in the use of the said connector for supplyingtalking currentto the talking: circuit established between the two subscribers. The current for ringing the ball at the called subscribers station comes from the ringing generator29 l, as shown in Fig. 3. All other current, however-that is to say, the current for both talking and switching purposescomes from the battery or centralized source or supply 61 at the central exchange. in the drawings, this bet tery is shownrepeate-d, or in different places, for convenience of illustration, as this species oat my invention is more easily illus tinted than the single battery form: but it will be readily understood that onebattery is preferably employed, and that its positive pole is grounded. Consequently, the current for operating the difierent relays and magnets all comes from the centralized source of is then fed through the talking 250 ohms resist and current from this same source connector to the circuit as soon as the connection is (ompleted between the two subscribers lines, and the called subscriber answers. In other words, and during conversation between; the two subscribers, the current necssary for talking purposes is led to this circuit from the battery 61 through the coils of relays F and H, and through the side-switch arms 324 and 325 and the shaftwipers 360 and 361 to the line of the called subscriber; the condensers 267 and 276, located in opposite re y,

sides of the talking circuit, preventing a flow of battery current in the opposite direction. At the same time, and owing" to the energizing of the relay H, current is supplied to the other part of the talking ccircuit that is to say, back to the calling subscribcrfrom the battery 61 through the coils ofrelay G, and through impedance 250 to one side of the circuit, and through the rotary-relay 235 to the other side of the circuit. In this way, and during the time that the subscribers are talking, the battery 61 is bridged across the talking circuit at points on each side or the condensers 267 and 276. And as the control-relayltl isonly energized when the called subscriber answers, as, for example, by removing his receiver, it is evident that no closed metallic battery circuit exists until the called subsciiber answers: and for this reason no talking current is furnished 7 from the battery to the talking circuit until both subscribers are sing their telephones. As shown, one battery furnishes talking current to the calling subscriber, and another battery furnishes talking current to the called subscriber; and the battery for the called subscriber energizes the means by which the other battery is bridged across the circuit to supply current to the calling; subscriber. As stated, these two batteries are preferably one, although for certain purposes, like long distance work, 1 may use two batteries, as shown. in other words, the centralized source of current supply can be made up of several batteries or sections. The first SQlQCllOl shown in Fig. i, and allotted to the subscribers apparatus at station B is, of course, similar to that shown in Fig. 1-. in Fig. l, however, the first selector is not in use, while that shown in Fig. 1 is in use; and at this juncture it will be seen that the second selector shown in Fig. 2 is also in use, and that the connector shown in Fig. 3 is in use. Throughout the different portions oi the diagram showing the connection between the two subscribers, the dark or heavy lines represent the subscribers line-conductors, and also the trunkli ne conductors, constituting the talking circuit.

At the subscribers stations,.'the arrangement is preferably such that the switch-hook lOll '39, for example, will close together the con tacts 7, '8 and 9 when the receiver is replaced, but not when the receiver is removed. In other words, these contacts 7, 8 and 9 are brought together for the purpose of releasing the 'difierent switches after the subscribers have finished their conversation, and are used for no other 'purpose.

Having thus described in a general way 1 both the construction and the operation of my improved central-energy automatic telephone system, the details of construction, and the functions of the different elements, will be best understood by considering the various operations and circuit connections which take place in connecting one subscribcrs line with another.

Suppose, for example, that sub-station #3321 desires connection with sub-station 26 #2241. The cailing subscriber will first remove the receiver 22 from switch-hook 39, Vhich act opens contacts 24 and 10 and closes contacts 2 1nd at. The subscriber Wili then, by means of any suitable calling device, twice close and break contact-point 37 with contact 35, thereby twice establishing momentarily, and twice sending an electrical current impulse over, the circuit from ground 1, through conductor 2, contacts 8 and 1, conductors 15, and 10, contacts and 37, conductors 1-1 and 48, circuit-changing switclrarm 66, circuit-changing switchpoint 77, conductor 102, el ctromagnetic relay 87, conductor 66, contact 5 1, armature 52, conductors'55 and 60, battery 61, condoctor 62 to ground 1 This causes "the electromagnetic reiay 87 to i" mature, ciose and breek contacts a twice, thus momentarily closing the cncuit from ground through conductor 93, contacts 01 and 88, conductor 101-, armature 124i, contact 123, conductors 121, 99 and 84:, circuitchanging switcherzn 6 1, circuit-changing switch-point 71, conductor 96, eiectro-niegnet 114, conductor 115, bettery 61, conductor-116th ground 1; and: which operation, resulting in a vertical step-by-step motion of the wipers, will ,lsce the said wipers 126,127, 128211111 129 et'ore, butnot in connection with, the second row of contacts leading to e 7 second. Jitter the two impulses are made as described, the ceiling device'will' ceuse connection to be made and brolnen between contactpoints 34 end 36, thus establishing a circuit from ground-l, conductor 2, contact-point 3 with contact-point 41, conductors 15, '20 end 10, contact 31 with contact 3' conductors42 and 49, circuit-changing switch-arin 67, cirwit-changing switch-point 80, electromagnetic relay 90, conductor 91, contact 53, armature 52, conductors 55 and 60, battery 61, conductor 62 to ground 1. This operation causes the electro-niagnetic relay 90 to attract its armature and close and break conselector-switch.

rec/sees tacts 89 and 92, thus establishing a circuit from ground *1, conductor 93, contacts 92 and 89, conductors 105 and 103, electro=inagnetic relay 106, conductor 107, battery 61, conductor 108 to ground 1, causing electromagnetic relay 106 to attract its armature, and causing armature 1% to engage contact 122, and breaking contact between armature 1241 and contact-point 123. struction of said electromagnetic relay is such thet,upon the attraction of its armature, and the release of same, the circuitchanging switch-arms 63, 61, 65, 66 and 67 are moved from contact-points 68, 71, 74, 77 and 80 to circuit-changing switch-contactpoints 69, 72, 75, 78 and 81, respectively, thus establishing, a circuit from ground 1, conductor 83, circuit-changing switch-arm 63, circuit-changing switch contact-point 69, conductor 95, eiectro-Inegnet 102, conductor 111, armature 110, conductor 112, battery '61, conductor 113 to ground 1, causing eiectro-Inagnet 109 to attract its eiz'inature.- In this way, the wiper-springs 126, 127, 128 and 129 are placed in contact with contactpoints 130, 131, 132 and133, thus establishing a circuit from ground 1, conductor 108, battery 61, conductor 107, relay 106, conductor 106, circuit-changing switch-contact-uoint 75, circuitchenging switch-arm 65, conductors and 100, wiperspring 127, contact 131, conductor 135, which, if there be another switch in connection with contact-point 131, wouhi c rnplete circuit to ground, causing; eleJtro-niarJ relay 106 to hold its'armoture f tracted position, and thus hoidi circuit-changing switchernis bore mentioned circuit-changing switj -contactpoints 69, 72, the, causing the arn'iature of eiectro-magnet 109 to continue to vibrate by means of opening and closing the circuit of said eie ctro-magnet at armature 110 and contact; 112, which causes the wipensprings to rotate until such time as a contact corresponding to 131 is found, to which no switch is connected, Upon the wiper-spring 127 closing this contact, the battery circuit through the private magnet or magnetic reiay 106 is broken, allowing said relay to react-causes circuit- 64, 65, 66 and 67 72, 75, 78 and 81 lease its armature, which changing switch-arms 63, to move from contacts 69,

to circuit-changing switch-contacts 70, 73, v

7 6, 79 end-82, thus grounding conductor 135 and contact-point 131 by means of the circuit from ground 1, circuit-changing switchcontact 76, circuit-changing switcherin 65, conductors 85 end 100, wiper-spring 127, contact-point 131 to conductor 135, thus pre-' venting the establishing, of. connection, by

e w per-spring 1261 any other switch, of th with contact 130; "wiper-spring 127 with contact 131; Wiper-spr1ng 128 with contact 132; wiper-spring 129 The coneiectro-magnetic with contact 1-1 33.

You

This also establishes connection from contact-point 37. conductors 41 and'48, circuit changing switch-arm 66, contact-point 79, conductor 101, spring-wiper 128, contact 132, conductor 136, and a connection from contact 36. conductors 42 and 49, circuit-changin; switch-arm 67, circuit-changing switc point. 82, conductor 125, wiper-spring 129, contact 133 to conductor 137, and connection from ground 1, conductor 120, battery 01, conductor 119, electro-magnet 118, conductors 117 and 97, circuit-changing switch contact-point 73, circuit-changing\switchrm 6-1. conductors 84 and 99, wiper-spring 126 with contact 130 and concluctor 131, which conncctssub-station #3321 with the second selector-switch (Fig. 2) by means of conductors 131, 136 and 137, which connect sub-station #3321 with the trunks leading to the second thousan1 group of substations. The subscriber at sub-station #3321 will then, by means of the calling clevice, close and break contacts 35 and 37 .wicc,saine as betore,-thus sending incmentarily electrical impulses from ground 1, conductor 2, contacts 3 and 1, contluc'tors 15, 20 ancl 10, contacts 37 and 35, conductors 11 and 18. circuit-changing switcharm 66, circuit-changing switch contactpoint 79, conductor 101, wiper-spring 128, contact 132, conductor 136, circuit-changing switch-arm 150 (Fig. 2), circuit-changing switch contact-point 102, conductor 183, elec tic-magnetic relay 18 1, conductors 182, 191, battery 01, conductor 195, to ground 1, thus causing electromagnetic relay 18 1to at-.

tract its armature, causing contact-points 185 and 187 to be closed and openedl twice, thus sending momentarily two impulses through electro-magnet 204 by means of: the

.circiiit from ground 1, conductor 189, contacts 187 and 185, conductor 173, relay-er mature 1174:, contact 175, conductors 197 and 170, circuit-changing switchers 1 18, circuit-changing switch contact-point 156, conductor 178, electro-inagnet 20 1, conductor 205, battery 01, conductor 206 to ground 1, which act by a resulting vertical step-bystep movement, places the wiper-springs 207, 208, 209 and 210 before, but not in contact with, contects'211, 212, 213 and 214-, respectively. As before .nuantiomerl after the calling device has closed and broken the contacts 35 c2112 37 the required number of times, the contacts 31 anti 38 are caused to be closed and openecl, thus establishing, momentarily, a circu t from grouncl 1. concluctor2, contacts3 anti 4, conductors 15, 20 and- 10, contactstie and 36,conductors 12 and 19, circuit-changing, switch-arm 07, circuit-changing switch contact-point 82,

= conductor 125, wiper-spring129, contact 133,

conductor 137, circuit-changing switch-arm 151, circuit-chang ng switch contact-point 165, conductor-191, electromagnetic relay lductor 195 to 190, conductors 192 and 194,battery 61, conground 1, This causes the electro-magnetic relay 190. to attract its armature, -an& closes contact 186 with contact 188, thus establishing a circuit from ground 1,.conrluctor 189, contact 188 to contact 186, conductors 170'and 169, electro-magnetic relay 500, conductor 171, battery 61, conductor 172 to ground 1, which act causes electromagnetic relay 500. to attract its armature; the construction of electromagnetic relay 500 being such that, upon the attraction and release of its armature, the circuit-changing switch-arms 117, 1 18, 119,150 and 151 break contact with circuit-changing switch contact-points 153, 156, 150, 162 and. 165, anol make contact with circuit-changing switchc'ontact-points 151, 157, 100, 103 and 100, respectively. Ubviously, this establishes a circuit from ground 1, conductor 152, circuit-changing switch-arm 117, circuit-changing switch contact-point 15 1-, conductor 177, electro-niagnet 198, conductor 200, armature 199, contact-point 201, conductor 202, battery 01, conductor 203 to groun 1; the construction of electro-magnet 198 being such that, upon the vibration of its armature, the wiper springs 207, 208, 209 ancl' 210 are caused to be closed in contact with line-contacts 211, 212, 213 and 21 1. 11 there be another switch in connection with contact 212, there will then be established a connection from ground 1, conductor 172, battery 01, conductor 171, elective-magnetic relay 500, conductor 169, circuit-changing switch contact-point 160, sirle-switch-wiper 119 and conductor 180, wiper-spring 208, contact 212 to conductor 216 to ground 1, through the switch in connection with said contact 212 (not shown), which will cause the circuitchanging switch-arms to be helcl in contact with the circuit-changing switch contactpoints iast mentioned, causing electro-rnagnet 198 to continue to vibrate its armature until spring 208 reaches a contact-point similar to 212, but with which there is no breaks the circuit through eiectro-mcgnet 198, thus causing it to cease vibrating and allowing wiper-springs 207, 208, 209 anfi 210 to remain in contact with contact-points 211, 212*, 213 anrl 211, thus establishing connection {from sub-station #3321 (Fig, 11 with con&uctors 217 curl 218, and also a con-= nection, from ground 1, circuit-cbanging switch contact-point 101, side-switch-wiper 1,19 ancl constrictor "180, wiperegaring 208,

contact 212 to conductor 215, end a connection from ground 1 to conductor 115, battery 61. conductor 14 1, electromagnetic relay 143, conductor 113, circuit-changing switch contact-point 158, circuit-changing switcharm 148,: conductor 179, Wiper-spring 237 contact 211 to conductor 215, and the estab-' lishing of connection between wiper-spring i308 and contact 212 with ground 1 prevents 1 seizure of contacts in multiple with the contacts 212, 213 end 2141, by any other 7 switch. A

A connection is thus established from telephone #3321 toiconcluctors 217 and 218 (Fig. 3) leading to a connector-switch representing the one hundred which the connection is to be completed. The subscriber at then, by means of the calling device, close and break contacts 35 enol 37 four times, thus sending momentary impulses from ground 1, conductor 2,. contacts 3 and 4:, conductors 15, and 1-0, contacts 37 and 35; conductors 11 and 18, circuit-changing switch-stun 66, circuit-changing switch contact-point 79, conductor 101, Wiper-spring 128, contact 132, conductor 136, circuitchanging switch-arm 153 (Fig. 2), circuits c 'ig' switch contactpcint 13 1,. couoluc- Wiperepriug 23%, contact 213, com

contract 254,-, conilcctcr 233, electropiety 225, conductor 22%, tor 213 to This i attract res 1 break (l contact-point- "es; and each use this contact suit is u reel from ground conductor contact 231, com se -rm. 227, conductor 2 1, armature 332, contact 331, conductor 323, circuit-changing arm circuit-changing arm contact-point 335, conductor 347, electro-msgnet 3 19, conciuctor 351, conductor 352, electric battery 31, conductor to grouncl 1, thus causing eiectro-msgnet 349 to sttract its iii-mature four times, which raises the Wiper-springs 350, 330 and 361 before, but not in contact with,zcoutacts 135, 4% e113 1-37, respectively. As before mentioned, after the calling device has closed and broken contacts 35 and 37 the required number of times, the ccntscts 3% and 33 are caused; to be closecl and 'ogeneci, thus establishing momentarily a circuir, from ground 1, conductor 2 to contacts 3 and i, conductors 15, 20 and 10, contests 31 end 36, conductors 12 and 49, circuit-changing switch-arm 67, circuit-changing switch-arm contact-point 82, conductor 125, wiper-springs 129, contact 133, conduc- J tor 137, circuit-changing switch-arm 151 (Fig. 2), circuit-changing switch-arm cou- 68 210, contact. 21%, c nduct rs 2 8 and 23 grou in V sub-station #3321 will tact-point 167, conductor 193, spring-wiper rasse ductors 251 and 275, armature 274, contactconductor 281, electric battery 61, conductor 282 to ground 1, thus completing the circuit and causing the electromagnetic relay 235 to momentarily attract its armature and thereby close and break contact between contact-arm 228 and contact point 233. 'l Vhen this contact is made, a circuit is established from ground 1 through conductor 232, contact-point 233, contact-arm 228, conductor" 222, 333, battery 61, conductor 334; to ground 1, thus causing electro-magnet 329 to momentarily attract its armature; and. the construction of electro-magnet 329 is such that this causes circuit-changing switch-arms 325, 324, 323 and 322 to leave the contactpoints 3 11, 3 11, 337 anti 335 and pass to contact-points 345, 342, 338 and 336. The subscriber at sub-station #3321 will then, by means of the calling device, close and break contacts 35 and 37 once, the same as before, thus again sending, momentarily, an elect-rical impulse from ground 1, conductor 2, contacts 3 end 1-, conductors 15, 20 and 10, contacts 37 and; 35, conductors 1-1 and 48, circuit-changing point 273,

switch-arm 33, circuitchanging switch-arm contactomb 73, conductor 101, spring 128, com. t 132, con- .ciuctor 136, circuit-chengi cuitschanging arm co ector 131, spr" 21?, 23a nit cc 332, contact-point 331, conductor 326, circuit-changing arm 322, contact-point 336, conductor 2&3, electromsgnet 359, conductor 353, conductor 352, battery 61, conductor 35% to ground 1, thus causing the electro-magnet 359 to momentarily attract its armature, which causes Wipers 350, 360 end 361 to close contact with contacts 195, 195 and 497, respectively. As before mentioneti, after the calling elevice has closed and broken contacts 35' and .37 the required number of times, contacts 34 and; 36 are caused to beclosed and opened, thus establishing, momentarily, a circuit from ground 1 to conductor 2, contacts 3 and 1, conductors 15, 20 and 40, contacts 34 end; 36, conductors 42 and 49, circuit-changing switch-arm 67, circuit-changing switch contact-point 82, conductor 125, spring-wiper 129, contact 133, conductor 137, circuitchanging contact-arm 151 (Fig. 2) circuitmade between contact-point 233 and contactarm 228, the circuit is established from ground 1 through conductor 232, contactpoint 233, contact-arm 228, conductor 222, clectro-maguct 329, conductor 333, battery 61, conductor 334 to ground 1; thus causing clectro-magnet 329 to momentarily attract its armature. lhe construction of electromagnet 329 is such that if, at this time, no

other switch be in connection with springwiper contact-points 495, 496 and 497, then, when electro-magnet 329 releases its armature 332, circuit-changing arms 322, 323, 324 and 325 will pass from contact-points 336, 338, 342 and 345 to contact-points 339, 355, 343 and 346; but if some other switch should be in connection with spring-wiper contactnoints 495, 496 and 497, then conductor 362 W111 be connected to ground 1 through the other switch by a circuit not shown; or if the subscriber at telephone #2241 should have, by operating tlie'calling device, made a connection, or have begun'to make a connection, to some other telephone, then contact-arm 409. (Fig. 4) will have broken contact from point410, and have closed contact with contact-point 408; thus establishing a circuit from ground 1 through conductor 411, contact-point 408, contact-arm 409, conductor 362 to contact 495 (Fig. 3), and connecting contact-point 495 to ground, as already mentioned. Contact-arm 409 is released by the first-selector as soon as its shaft is raised one step. If contact-point 495 should be connected to ground, by either of the means already described, then when electro-magnet 329 attracts its armature circuit-changing contact-arms 322, 323, 324 and' 325 will not pass from contact-points 336, 338, 342 and-345 to contact-points 339, 355, 343 and 346; but a circuit will be established from ground through conductor 362, contact 495, spring-wiper 350, conductor 340, "circuit-changing arm 323, circuitchangiug arm contact-point 338, conductor 237, contact-point 234, contact-arm 229, conductors 223 and 258, electro-magnet 254, conductor 256, battery 61, conductor 257 to ground 1; thus causingelectro-magnet 254 to attract its armature. The construction of the devices-operated by this magnet is such that, when it wipers 350, 360 and 361 will brealg contact from contacts 495, 496 and 497, and will be attracts its armature, springrestored to normal position; and circuitchanging arm-s 322, 323, 324 and 325 will pass from contact-points 336, 338. 342 and 345 to their original positions, making contact with points 335, 337. 341 and 344, respectively. The subscriber at telephone #3321 will, at this time, by means of a push-button on telephone #6. 321, press contact-arm 16 (Fig. 1) against contact-point 19 in an endeavor to ring the hell on telephone #2241; and when contact is closed between contact-arm 16 and. contact 19, circuit will be established from ground 1. conductor 2, contact-arm 3, contact-point 4, conductor 15, coutact-point 19 to contactarm 16, conductor 365, contact-arm 6, contact-point 501, contact-arm 5, conductor 138, transmitter 14, conductors 13, 411 and 48, circuit-changing arm 66, circuit-changing arm-contact 79, conductor 101, spring-wiper 128, contact 132, conductor 136, circuitchanging arm 150 (Fig. 2), circuit-changing arm-contart 164, conductor 181, spring-wiper 209, conductors 213, 217, 239 (Fig. 3), conductor 266, armature 265, contact-point 264, conductor 238, clect-ro-magnetic relay 225, conductor 224, battery 61, conductor 219 to ground 1; thus causing electro-magnetic relay 225 to attract its armature, and to make contact with contact-point 231 to contact-arm 227, and thus establishing a circuit from ground 1 to conductor 232, contact-point 231, contact-arm 227, conductor 221, armature 332, contact-point 331, conductor 326, circuit-changing arm 322, circuit-changing arm contact-point 335, conductor 347", electro-magnet 349, conductors 351 and 352, battery 61, conductor 354 to ground 1. This causes 'electro-magnet 349 to attract its armature, and the construction of the devices operated by clectro-magnet 349 is such that, when it attracts its armature, it causes the shaft to close contact between contact-arm 319 and contact-point 318; and when contact is made between con-- tact-arm 319 and contact-point 318, this establishes a circuit which gives a busy signal to subscriber at telephone #3321 from ground 1 through conductor 308, conductor 314, inductiou-coil-winding 313, conductor 311, induction-coil 312, colidurlor 315, condenser 316, conductor 317, contact-point 318, contact-arm 319, conductor 321,

changing arm contact-point 341, circuit:- changing arm 324, conductor 327, armature 291, contact 290,0onductor 289, condenser 267, conductors 239 and 217, contact 213 (Fig.2), spring-wiper 209, conductor 181, contact 164, circuitchanging arm 150, conductor 136, contact 132 (Fig. 1), wiper 128, conductor 101, contact 79, circuit-changing arm 66, conductors 48, 41 and 13, transmitter 14. conductor 138, contact-arm 5,, contact 501, contact-arm 25, receiver 22, conductor 21, coil 26, conductor 28, condenser- 30 concircuit ductors 32, 33, 42 and 49, circuit-changing arm 67, contact 82, conductor 125, wiper" 129, contact 133, conductor 137, circuitchanging arm 151, contact 167, cnnductor 193, spring-wiper 210, contact 214, conductors 218-and 236 (Fig. 3), electro-magnetic relay 235', conductors 251 and 275, armature 274, contact 273, conductor 281, battery 61, conductor 282 to ground 1; thus completing a circuit for the signal-current induced by circuit-breaking mechanism 310, battery 61 and induction-coil-winding 313 in inductioncoil-Winding 312 through the receiver of telephone #3321, which gives thesubscriber at telephone #3321 a signal informing him that telephone #2241 is busy.

If telephone #2241 is notbusy, and conductor 362 is therefore not connected to ground (Fig. 4) at the time circuit-changing arms 322, 323, 324 and 325 are resting on contacts 336, 338, 342 and 345, and if at the same time electro-magnet 329 attracts its armature, then the construction of electromagnet 329 is such that the crcuit-chan ing arms 322, 323, 324 and 325 will pass rom .contact-points 336, 3,38, 342 and 345 to contact-points 339, 355, 343 and 346. The effect of this will be to complete a circuit from ground 1 throughcoriductor 356, contact 355, circuit-changing arm 323, conductor 340,

spring-wiper 350, contact 495 to conductor 362, thus establish ng, on conductor 362, a guarding potential which will prevent any other switch (by means not here shown) from making a connection to conductor 362 until conductor 362 is again disconnected from ground. Completing the circuit from ground 1, this conductor 362 also establishes the circuit from ground to'conductor 362, in the manner already described, and thence to contact-arm 409 (Fig. 4), contact 410, elec tro-magnetic relay 412, conductor 420, battery 61, conductor 421 to ground 1; thus causing theclectro-magnetic relay 412 to attract its armature and open the contacts between armature 413 and contacts 414 and 415, and thus disconnecting the bridge between conductors 363 and 364 formed through circuit-changing arm 42?, contact 440, conductor 451, electro-magnctic .relay 449, conductor 418, contact 414, armature 413. contact 415,'cond'uctor 416, electro-lnagnetic relay 444, conductor 450, contacts 438' and 437, circuit-changing arm 426 to conductor 363. The signaling circuit is now established from telephone #3321 to telephone #2241, and subscriber at telephone -#3321 can ring the bell 381 ontelephone #2241 by closing contact between contactarm 16 and contact-point 19 at telephone #3321 (Fig. 1). Momentarily closing this contact-establishes a circuit from ground 1 through conductor 2, contact'arm 3, contact 4, conductor 15, contact 19, contact-artn 16, conductor 365, contact-arm 6, contactl 501,

aavaoea conductors 13, 41 and 48, circuit-chan ing arm 66, contact 79, conductor 101, sprin wiper 128, contact 132, conductor 136, circurt-changing arm 150 (Fig. 2), contact .164, conductor 181, spring-wiper 209, contact 213, conductors 217 and 239 (Fig. 3), conductor 266, armature 2 65, contact 264, conductor 238, electro-magnetic relay 225, conductor 224, battery 61, conductor 219 to ground 1; thus momentarily establishing a circuit from battery through electro-magnetic relay 225 and causing it to attract its armature, closing circuit. between contact 231 and contact-arm 227. The effect of closing contact between contact 231 and contact-arm 227 will be to establish a circuit from ground 1 through conductor 232, contact 231, contactarm 227, conductor 221, armature. 332, contact-point 331, conductor 326, circuit-changing arm 322, contact 339, conductor 328, electro-magnetic relay 301, conductor 302, battery 61, conductor 303 to ground 1; thus establishing a circuit fr6tn' battery 61 through electro-magnetic relay 301, causing it to attract its armatures and breaking conneotion between contact, 290 and armature 291, and between contact 297 and armature 299, and to close contact from armature 291 to'contact-point 292, and from armature 299 to contact-point296 The effect of clos:ng

these contacts will /beto ring the bell on telephone #2241, b completing the circuit from ringing machi e 294 to conductor 29.3,

contact 292, armature 291, conductor 327, circuit-changing arm 324, contact 343, conductor 357, spring-wiper 360, contact 496, conductors 363 and 406 (Fig. 4), conductor 502, vibrating bell 381, conductor 380, contact 375,- contact-arm 376, conductor 391, can

denser 397, conductors 400, 401, 407 and 364,

contact'497 (Fig. 3), spring-wiper 361, conductor 358, contact 346, circuit-changing 'armatures, and through electro-magnetic relay-coils 286 and 287, but not causing them to attract their annatures because the coils 286 and 287 are so constructed as to neutraliae each other. Circuit from battery through these coils comprises the following connections: from battery 61 through conductor 261, coil 268, conductor 280, coil 286, conductors 288 and 289, contact 290, earmature 291, conductor 327, circuit-changing arm 324, conductors 343 and 357 springwiper 360, contact 496, conductors 363 and 406 (Fig. 4), concluctor382, transmitter 366, conductor 367, contact-arm 371, contact 372, contact-arm 373, conductor 393, contact-arm 385, contact 386, conductor 387, inductioncoil 396, conductors 401, 407 and 364, contact 49'", (Fig. 3), spring-wiper 361, conductor 358, contact 346, contact-arm 325, conductor 300, armature 299, contact 297, conductors 298 and 285, coil 287, conductor 279, coil 269, conductor 262, battery 61; thus completing a circuit through electro-mag netic coils 268,- 269, 286 and 287, causing magnets 268 and 269 to attract their armatures, and also sending an electric current through transmitter 366 and induction-coilwinding 396 of telephone #2241 (Fig. 4); thus furnishing current for the talking circuit of telephone #2241. When coils 268 and 269 attract their armatures 265 and 274,

contact is broken between armature 265 and conductor contact-point 264, and established between armature 265 and contact-point 263; and contact is also broken between armature 274 and contact-point 273,.and established between armature 274 and contact-point 272, thus completing a circuit from the battery 61 to electro-magnetic coils 245 and 270, furnishing electric current at telephone #3321 for the talking circuit. This circuit includes the following connections: battery 61, conductor 243, 0011 270, conductor 247, contact 272, armature 274, conductors 275 and 251, electro-magnetic relay 235, conductors 236 and 218, contact 214, springwiper 210, conductor 193, contact-point16 conductors 151 and 137, contact 133 (Fig.

1), spring-wiper 129, conductor 125, contact 82, circuit-changing arm 67, conductors 49, 42, 33 and 31, induction-coil-winding 27, 18, contact 17, contact arm 16, conductor .365, contact-arm 6, contact 501, contact-arm 5, conductor 138, transmitter 14, conductors 13, 41 and 48, circuit-changing arm 66, contact 79, conductor 101, spring-wiper 128, contact 132, conductor 136, circult-changingarm 150, contact 164, conductor 181, spring-wiper 209, contact 213,

conductors 217 and 239 (Fig. 3), conductor '266, armature 265, contact 263, conductor 259, impedance coil 250, conductor 246, coil 245, conductor 271 to the other terminal of the batter 61. It willbe seen that the'cunrent supp ied for talking purposes to. the calling subscribers line passes through three other coils- 250 and 245 and 270-besides the coil 235, while the voltage of the com mon battery remains constant; This reduces thecurrent through said coil to such an extent that the magnetic power developed therein is not sufficient to attract 18S armature against the tension of springs 228' and 229. Connections are now so completed sistances will be set up in the circuit just described from battery 61 through transmitter 366 and induction-coil-winding 396; and the effect of this will be to send variable currents through induction-coil-winding 396, thus inducing currents in induction-coilwinding 395. These variable currents will be carried to telephone #3321 over the tollowing circuit, and also through the receiver 0? telephone #2241: induction-coil 395, conduetor 389, receiver 394, conductor 392, contact-arm 374, contact-arm 37 3, contact 372, contactarm 371, conductor 367, transmitter 366, conductors 382, 406, and 363, contact 496 (Fig. 3;), spring-wiper 360', conductor 357, contact 343, circuit-changing arm 324, conductor 327, armature 291, contact 290, conductor 289, condenser 267, conductors 239 and 217, contact 213 (Fig. 2), spring-wiper 209, conductor 181, contact 164, circuitchanging arm 150, conductor 136, contact 132 (Fig. 1), spring-wiper 128, conductor 101, contact-point 79, circuit-changing arm 66, conductors 48, 41 and 13, transmitter 14, conductor 138, contact-arm 5, contact 501, contact-arm 6, contact-arm 25, conductor 23,

receiver 22, conductor 21, induction-coil- 3), conductor 298, contact-point 297, armature 299, conductor 300, circuit-changing arm 325, contact-point 346, conductor 358, spring-wiper 361, contact 497, conductors 364 and 407 (Fig. 4), conductors 401 and 400, condenser 397, conductor 443 to the other end of induction-coil-windin 395, thus completing the circuit. Similar y,-currents will be induced in the circuits just described between the two tele hones passing through the receivers oi bot telephones if subscriber at telephone #3321 should speak into transmitter 14, thus causing variable resistance to be set up in the circuit already described from'battery 61 through electromagnetic relay coils 245,-,and 270 (Fig. 3) to transmitter 14 an duction-coil-winding 27.

When conversation is "completed between the subscribers at the two telephones, the

placing their receivers on the switch-hooks,

thus causing these hooks to return to nor- 1 o cuit-c mal position; but if subscriber at telephone #3321 (Fig. 1) returns to normal position,

connection is made, momentarily, between contact-arm 7 and contact-points 8 and 9, thus completing a circuit from ground 1 to conductor 2, contact-arm 3, contact-point 4, conductors 15 and 20, contact-point 9, contact-arm 8, contact-arm 7, conductors 32, 33, 42 and 49, circuit-changing arm 67, contactpoint 82, conductor 125, spring-wiper 129, contact 133, conductor 137, circuit-changing arm 151 (Fig. 2), contact 167, conductor 193,,spring-w1per 210, contact 214, conductors 218 and 236 (Fig. 3), relay-coil 235, conductors 251 and 27 5, armature 274, contact-point 272, conductor 247, electro-magnetic relay-coil 270, conductor 243, battery 61, conductors 271' and 244 to ground 1; thus completing the circuit from battery 61 through electro-magnetic relay-coil 235, causing it momentarily to attract its armature, and also energizing coil 270, causing this coil to attract its armature 249, because electro-magnetic relay-coil 245 will no longer neutralize electro-magnetic relay-coil 270, inasmuch as the circuit, already described, through these coils, from battery 61 and through telephone #3321, was changed by both lines being momcntaril grounded at telephone #3321 when the subscriber placed his receiver on the hook, thereby short-circuiting the coils 245 and 250 through ground, as follows: from ground 1 at station A to conductor 2, spring 3, contactpoint 4, conductors 15 and 20, springs 9, 8 and 7 to conductor 13, spring 37, conductors 41 and 48, circuit-changing-arm 66, contact-point 79,- conductor 101, wiperspring 128, contact 132, conductor 136, ciranging-arm 150 (Fig. 2), contactpoint 164, conductor 181, wiper-spring 209, contact 213, conductors 217,239 and 266 (Fig. 3), armature 265, contact-point 263, conductor 259, coil 250, conductor 246, coil 245 to ground terminal 271 of battery 61. When coil 270 (Fig. 3) momentarily attracts its armature 249, contact is made between armature 249 and contact-point 241, thus momentarily establishing a circuit from ground 1 to conductor 242, armature 249, contactpoint 241, conductors 240 and 238, electromagnetic relay-coil 225, conductor 224, battery 61, conductor 219 to ground 1, and thus causing electro-magnetic relay-coil 225 to attract its armature and make connection between contact-arm 226 and contact-point 230, and also between contact-arm 227 and contact-point 231. Armature of electromagnetic relay-coil 235 also being attracted at the same tlme, as just described, contact will be closed between contact-arm 228 and contact-point 233, thus completing a circuit from ground 1 to conductor 232, contact 233, 4

contact-arm 228, conductor 222, electromagnetic coil 329, conductor 333, battery 61, conductor 334 to ground 1, and thus completing a circuit from battery 61 through ductor 256, battery 61, conductor 257 to ground 1, and causing electro-magnetic coil 254 to momentarily attract its armature The construction of this coil 254 is such that, when it momentarily at tracts its armature, the parts of the connector-switch (circuits of which are shown in Fig. 3) will be returned to their normal positions at the same time the circuits are momentarily closed, which will return the parts of the first and second selectors to theirnormal positions. This circuit is as follows: from ground 1 through conductor 252, contact-point 253, armature 255, conductor 248, contact-point 230, contact-arm 226, conductors 220 and 215, contact-point.

211 (Fig. 2), spring-wiper 207, conductor 179, contact-arm 148, contact 158, conductor 146, coil 143, conductor 144, battery 61, conductor 145 to ground 1, thus momentarily closing circuit from battery 61 throug elcctro-magnetic coil 143, causing it to -momentarily attract its armature. The construction of coil 143 is such that, when it momentarily attracts its armature, the parts of the second selector (circuits of which are shown in Fig. 2) will be returned to their normal ositions, and at the same time contact Wlll be momentarily made between contact-point 142 and armature 141, thus completing the circuit from ground 1 through conductor 140, contact 142, armature 141, conductor 134, contact-point 130 (Fig. 1), spring-wiper 126, conductors 99 and 84, contact-arm 64, contact-point 73, conductors 97 and 117, electro-magnetic coil 118, conductor 119, battery 61, conductor 120- to ground 1, thus completing circuit from battery 61 through electro-magnetic coi'l 118, and causing it to momentarily attract its armature, which returns the parts of the first selector-snitch to their normal positions. If the subscriber at telephone #2241 places the receiver on the switch-hook before subscriber at telephone #3321 has replaced the receiver,-then, as the hook returns to normal position, breaking contact between contact-point 372, contact-arm 373 and contactarm 374 (Fig. 4), it will thus break the circuit heretofore described from battery 61 nuance through electro-magnetic coils 268 and 269 (Fig. 3) whereupon the armatures of these coils will return to normal positions, breaking contact between armature 265 and con tact-point 263, and closing contact between armature 265 and contact-point 264, breaking contact between armature 274 and contact-point 272, and closing contact between armature 274 and contactoint 27 3. It armatures 265 and 274 shoul have returned to their normal positions before the subscriber at telephone #3321 replaces the receiver on the switch-hook, then the parts of the connector-switch, instead of being restored to their normal positions by the closing of circuits as above described, will be restored by the closing of the following circuits: As

the switch-hook on telephone #3321 descends contact will be made, as already described, between contact-arm 7 and contactpoints 9 and 8, thus closing circuit from ground 1 at telephone #3321 through both electro-Inagnetic relay-coils 225 and 235 (Fig. 3), causing them to momentarily attract their armatures. These circuits are as follows: from ground 1 (Fig. 1) through conductor 2, contact-arm 3, contact-point 4, conductors 15 and 20, contact-point 9, contact-arm 7, conductors 139, 13, 41 and 48, circuit-changing arm 66, contact 79, conductor 101, spring-wiper 128, contact 132, conductor 136, circuit-changing arm 150, contact 164, conductor 181, spring-wiper 209, contact 213,, conductors 217 and 239 (Fig. 3), conductor 266, armature 265, contact-point 264, conductor 238, electro-magnetic relay-coil 225, conductor 224, battery 61, conductor 219 to ground 1; thus completing the circuit from battery 61 through coil 225, causing it to momentarily attract its armature, as already mentioned. The circuit through coil 235 is as follows: from ground 1 (Fig. 1) through conductor 2, contact-arm 3, contact 4, conductors 15 and 26, contact 9, contact-arm 7, contact-point 8, conductors 32, 33, 42 and 49, circuit-changing arm 67, contact 82, conductor 125, sprin -wi er 129, contact 133, conductor 137, circuit-changing arm 151 (Fig. 2), contact 167, conductor 193, spring-wiper 210, contact 214, conductors 218 and 236 (Fig. 3), coil 235, conductors 251'and 275,.armature 274, contact. 273, conductor 281, battery 61, conduct-or 282 to ground 1, thus completing the circuit from battery 61 to coil 235. \Vhen coils 235 and 225 are thus momenta- .rily ener ized at the same time, completed in the manner previously described, energizingcoil 254 (Fig. 3), cansingit to restore parts of the connectorswitch to normal position, and also-causing it to momentarily close circuit in the manner alreadydescribed, which will cause arts of the first andsecond selector-switc ice to be restored to normal position. If operator circuits are at telephone #3321 should neglect, for some time, to replace the receiver on the switchhook, and thus fail to cause the parts of the first selector, second selector and connector switches to be restored to their normal positions, the construction of the connector-switch, and of telephone- #2241, is such that the subscriber at telephone #2241 can then restore the parts of the connector-switch connected to the conductor to their normal positions, thus frecing the conductor and making it possible to call and to be called by other subscribers. This restoration of the parts of the connector-switch is effected as follows: By use of the calling device (not here shown) the subscriber at telephone #2241 (Fig. 4) can close contact between contact-arm 402 and contact-point 403, at the same time breaking contact between contact-point 372, contact-arm 373 and contact-arm 374; and when contact is broken between contactpoint 372 and contact-arms 373 and 374, then the circuit previously described from battery 61 (Fig. 3) through coils 268, 269, 286 and 287 is open, and those coils are no longer energized, and, therefore, when contact 403 is closed with contact-arm 402 (Fig. 4), and the circuit is thus momentarily completed from battery through coil 287 (Fig, 3), this coil will momentarily attract its armature 283.

The circuit from battery through coil 287 is as follows: from ground 1 (Fig. 4) through conductor 368 to contact-arm 369, contact 370, conductors 384, 390 and 398, contact 403, contact-arm 402, conductors 407 and 364, contact 497 (Fig. 3), spring-wiper 361, conductor 358, contact 346, circuitchanging arm 325, conductor 300, armature 299, contact-point 297, conductors 298 and 285, coil 287, conductor 279, coil 269, conductor 262, battery 61, conductors 261 and 260 to ground 1, thas completing the circuit already mentioned from battery 61 through coil 287, energizing this coil, and causing'it to closing circuit from ground 1 through conductor 284. armature 283, contact 278, conductors 27 7 223 and 258, coil 254, conductor 256, battery 61, conductor 257 to ground 1 and momentarily energizing coil 254 which, as already mentioned, is of such construction that, when it momentarily attracts its armature, parts of the connectorswitch are restored to normal position. Among other things, spring-wiper 350 breaks contact with contact 495, thus breaking the circuit between ground 1 and conductor 362, and tbus'rclieving conductor 362 of the guarding potential which was placed thereon at the time connection was completed between telephones #3321 and #2241. \Vhen this guarding potential is removed, conductor 362 is thus lett open, so that con.

attract its armature 283; thus nections canbe made to it hector-switches; and the circuit heretofore of bridges is reduced to a minimum in ator 421 to ground 1 is also .tion, thus again closing by other con described from ground 1 through conductor 362, contact-arm 409 (Fig. 4), contact 410, coil 412, conductor 420, battery 61, conducopen, and the armature of coil 412 returns to normal posicontact' between armature 413 and contact-points 414 and 415, and again bridging the coils 444 and 449 across conductors 363 and 364, making it possible for subscriber attelephone #2241 to call any other subscriber.

It will thus be seen that an additional trunk-line conductoris used, in conjunction with afourth bank of contacts on each selector, for releasing between switches. In this way, no part of the release-circuit between switches includes any portion of the talking circuit, and consequently the bridges atthe selectors are cut off or opened up during conversation between the subscribers, and are not at this time left across the circuit. For this reason, the talking circuit includes no inductive resistance in the path of the talking currents, nor does it have any bridges at the selectors. Of course, there are necessarily one or more bridges left across the talkingcircuit at the connector; mt even so, it will be seen that the number system in which the talking'circuit contains no inductive resistance or coils in the path I transmitting switches,

. otl

F inductive resistance of the talking currentsthat is to say, no or coils in series in the talking circuit at any points between the and receiving ends of the circuit. In other, words, the additional wipers on the switch-shafts of the selectors, and additional bank of contacts in each selector, have only one function, to wit, the closing of the release-circuit at certain normally open points.

current, both for talking purposes and for operating the various relaysan'd magnets included in the selector and connector is all furnished from a battery or ier common source of supply at the central station; and as a matter of special improvement, the current for talking purposes is supplied to the circuit through the cone5 t s a e of the-welLlmown and well-undernector, and through connections which are controlled by the called subscriber. In other words, the current for talking purposes is supplied to neither subscribers line before the called subscriber answers the call and completes the talking circuit by taking down In this way, there is, as prelus receiver. viously stated, no closed metallic circuit until the called subscriber answers the call, .and no flow of talking current 111 the circuit until everything is in readiness for its use by the two subscribers.

As shown in Figs. 1, 2 and 4, the selec- Furthermore, the

other and also stood type. For example, these selectors may be of the general type shown and described in Patent No. 815,321, granted March 13, 1906, to Keith, Erickson and Erickson.

In Fig. 5, the first-selector is shown more in detail, and its eneral construction and operation are as follows: The shaft (J, in addition to having the previously described shaft-wipers 126, 127, 128 and 129, is also provided with the circular or so called vertical-ratchet-teeth c, and with the longitudinal or so-called rotary-ratchetteeth 0 the latter being arranged immediately below the. former. Just below the said "rotary-ratcllet-teeth, the shaft is also provided with a cam 0 adapted, before the shaft rotates, to limit the movement of the side-switch when the latter makes the first stepthat is, when the side-switcharm 0 advances the previously described side-switch-wipers 63, 64, 65, 66 and 67 from their first or normal position toitheir second or intermediate position. The vertical-ratchet-teeth 0 are provided with a longitudinally-extending groove or channel 0 adapted normall to engage the'stationary rest or supporting-dog 0 the latter having a hook-shaped end portion adapted to project within said groove or channel. With this arrangement, the said shaft can only move up and down while the said rest is in engagement with the said groove or channel; but the relative formation of the said rest and vertical-ratchet-teeth" is such that the shaft, when raised to any particular level, can then rotate in a step-by-step manner, its position at such level being maintained by the engagement of the end of the rest with the under side. of one of the ratchet-tee'ththat is, when the shaft is raised to the first level, the said rest then engages the under side of the first or uppermost ratchet-tooth when the shaft commences to rotate. Consequently, the shaft is always positively supported by the said rest-when the shaft is elevated. from its normal position-and regardless of the particular level at which the rotation is taking place. The shaft-wiper 126 is adapted to engage any one of the one hundred contacts arranged in ten horizontal rows of ten coninto engagement with any one of 'the one hundred contacts arrange in ten horizontal rows of ten contacts each in the so-called private-bank 0 The wipers 126 and 127 are, of course, insulated from the shaft; The well-known vertical and rotary line vipers 128' and 129, mounted upon the said shaft and insulated from each from the shaft, areaclapted to engage any one of the one hundred-, or

release-trunk-bank 0. 

